ALBUMINS OR PROTEINS. 271 



after Kirk 1 had previously shown that a crystallized acid could be obtained 

 from the urine of three children in the same family. He soon recognized 

 the fact that it was a mixture of uroleucic acid and uroxanthic acid. The 

 latter is, undoubtedly, identical with the homogentisic acid of Wolkow and 

 Baumann, who have established its constitution. 2 It is a di-hydroxy- 

 phenyl-acetic acid. Uroleucic acid, on the other hand, is a di-hydroxy- 

 phenyl-lactic acid. The latter has only occasionally been found in alcap- 

 tonuric urine, and is, undoubtedly, the antecedent of homogentisic acid. 

 Wolkow and Baumann have discovered the source of these acids, and also 

 the conception of the whole phenomenon. Alcaptonuria is not to be looked 

 upon as a disease; it is more to be considered as indicative of an anomalous 

 metabolism, which, without causing any noticeable derangement, may 

 continue for the entire lifetime. It is of considerable interest to note its 

 appearance in several members of the same family. As far as the origin 

 of the homogentisic and uroleucic acids are concerned, it is natural to 

 look to the aromatic groups derived from the albumin molecule. We 

 have already called attention to the fact that a large number of decompo- 

 sition products may be obtained directly from this source and appear in 

 the urine. 



Tyrosine, until recently, was the only elementary, aromatic constituent of 

 albumin, which was invariably found present and easily obtained. From it 

 are derived p-hydroxy-phenyl-propionic acid, p-hydroxyphenylacetic acid, 

 p-cresol and phenol. Wolkow and Baumann, by means of feeding experi- 

 ments, showed that the acids of alcaptonuric urine were also formed from 

 tyrosine. They found that the administration of tyrosine to a man afflicted 

 with alcaptonuria caused an appreciable increase in the amounts of alcap- 

 ton acids excreted. Wolkow and Baumann also indicate phenyl-alanine 

 (phenyl-amino-propionic acid ) 3 as another source of these alcapton acids. 

 These investigators did not have a sufficient quantity of this aromatic acid, 

 and they had to confine their researches to the relation of the alcapton 

 acids to tyrosine. The methods recently introduced by Emil Fischer, 

 for the isolation of the cleavage-products of proteins, made it possible not 

 only to obtain phenyl-alanine in larger quantities, but also showed its 

 universal distribution as an elementary constituent of albuminous sub- 

 stances. Very little albuminous material is free from it, and it is even 

 more widely distributed than tyrosine. On the basis of this knowledge, 

 and because of the recent discovery of the easy accessibility of phenyl- 

 alanine, the relations between it and the alcapton acids have been inves- 

 tigated anew. W. Falta and Leo Langstein 4 found that when this amino 



1 Kirk: Brit. Med. Jour. 2, 1017 (1886); J. Anat. and Physiol. 23, 69 (1889). 



2 E. Baumann and S. Fraenkel: Z. physiol. Chem. 20, 219 (1894). 



3 M. Wolkow and E. Baumann: loc. cit. p. 266. 



4 W. Falta and L. Langstein: Z. physiol. Chem. 37, 513 (1903). 



